1. Field of the Invention
This invention relates to silicone sealants which cure upon exposure to moisture comprising an alkoxysilethylene endblocked polydiorganosiloxane, alkoxy functional crosslinker, and titanium catalyst.
2. Background Information
Silicone sealants, of the type in which an alkoxy endblocked polymer is reacted with an alkoxy functional crosslinker in the presence of a titanium catalyst, having a greatly improved shelf life have been developed by use of a trialkoxysilalkylene endblocked polymer. These sealants have the desired improved shelf life, but in many cases have a modulus which is too high for the application.
One solution to this problem is taught in U.S. Pat. No. 4,687,829, issued Aug. 18, 1987, in which alkoxy functional polydiorganosiloxane having alkoxysilethylene ends is mixed with a combination of trifunctional or tetrafunctional silane crosslinker and difunctional silane chain extender. The cured composition can be adjusted for the desired elongation by varying the ratio of crosslinker to chain extender, but there must be at least 50 mole percent of crosslinker in the composition to ensure that the composition cures to a non-tacky surface.
A method of producing a one-part silicone elastomeric sealant which has improved shelf life in taught in U.S. Pat. No. 4,711,928, issued Dec. 8, 1987. This method mixes a diorganovinylsiloxy endblocked polymer, reinforcing filler and silazane, then converts the polymer to an alkoxysilethylene ended polymer by reaction with an alkoxy functional silane.
Another method of controlling the modulus of silicone sealant having alkoxy functionality and using a titanium catalyst is disclosed in this invention.